High Efficiency Video Coding (HEVC) is a video coding standard under development with the goal to achieve additional 50% bit-rate reduction over the existing H.264/AVC standard. HEVC is block-based hybrid video coding with very flexible block structure. Three block concepts are introduced in HEVC: coding unit (CU), prediction unit (PU), and transform unit (TU). The overall coding structure is characterized by the various sizes of CU, PU and TU in a recursive fashion, where each picture is divided into largest CUs (LCUs) consisting of 64×64 pixels. Each LCU is then recursively divided into smaller CUs until leaf CUs or smallest CUs are reached. Once the CU hierarchical tree is done, each leaf CU is subject to further split into prediction units (PUs) according to partition type. Furthermore, transform is applied to TUs to transform the spatial data into transform coefficients for compact data representation.
For transform processing in current HEVC, a hierarchy RQT (Residual Quad Tree) is used. The TU size is related to the CU size, but is independent of the PU size. Since the TU partition is independent of the PU partition and the maximum allowed TU depth, i.e., max RQT depth, is 3, the current syntax for residual quad tree, transform_tree( ), is quite complicated. This results in high encoding complexity and also causes increased time for processing the residual quad tree syntax. Furthermore, some syntax elements related to the transform tree such as max RQT depth for the INTER mode, max RQT depth for the INTRA mode, max TU size and min TU size have to be sent in the sequence-level (SPS) header. Accordingly it is desirable to develop a TU presentation scheme that will result in reduced complexity. Also, the current computation associated with selecting the best merge candidate for the 2N×2N CU merge mode is rather intensive. Therefore, it is desirable to reduce the computational complexity for selecting the best merge candidate for the 2N×2N CU merge mode.